This disclosure relates generally to global positioning system (GPS) satellite receivers, and more particularly, to an overall architecture thereof and to specific digital signal processing sections within such receivers.
GPS satellites transmit spread spectrum signals on L1 and L2 frequency bands at 154fo and 120fo respectively, where fo=10.23 MHz. Each of L1 signals is modulated by C/A code and P-code, which are unique for each satellite. Both codes are publicly known. Each of L2 signals is modulated by P-code only. Although both the C/A code and P-code sequences are known, each GPS satellite is provided with the capability of modulating its P-code with a secret signal generally referred to as W-code. This “anti-spoofing” (A/S) allows the GPS system to be used for military applications by preventing jamming signals based on known P-codes from being interpreted as actual GPS signals. The combination of the P-code and the W-code is typically referred to as the Y-code.
There are important advantages to obtaining access to both L1 and L2 signals. First, ionospheric refraction can be measured and removed by co-processing the L1 and L2 pseudorange, which allows achieving higher accuracy in stand-alone applications. Second, for survey applications, there is a significant advantage with the use of carrier-phase measurements of both L1 and L2 signals in phase-differential systems. L2 carrier-phase measurements supplemental to those of L1 redouble the total number of observables, and make it possible to arrange so-called “wide lane” observables that significantly improve performance of phase ambiguity resolution.
However, existing systems and methods for handling L1 and L2 signal have disadvantages. In particular, for example, existing techniques of recovering L2 carrier phase from the Y-code are becoming obsolete as GPS systems evolve. For example, known receiver structures are unable to exploit the possibilities of the new, more robust L2c code which will become available to civilian users. Known receiver structures are typically difficult or impossible to adapt to new applications because they are implemented by application specific integrated circuits (ASICs). Further, such ASICs can be costly.
Additionally, known receiver structures typically consume power and other resources at a high level in order to process L1 and L2 signals in an acceptable manner. Accordingly, there is a need for a processing method and system that retains high quality while reducing hardware complexity.